Internal combustion engines typically use hydraulic valve lash adjusting lifters to maintain a zero valve clearance. Older style solid lifters maintain a small clearance between the valve and its rocker or cam follower. These solid lifters wear and must be adjusted periodically so that the clearance is not so great as to lead to undesirable levels of tappet noise, a clacking sound. With the hydraulic lifter, pressurized engine oil is supplied to hydraulic valve lash adjusting lifter through a small hole in the lifter body. When the engine valve is closed (lifter in a neutral position), the lifter is free to fill with oil thereby increasing the length of the lifter. As the camshaft lobe enters the lift phase of its travel, it compresses the lifter piston, and a valve shuts the oil inlet. Oil is nearly incompressible, so this greater pressure renders the lifter effectively solid during the lift phase. As the camshaft lobe returns to its base circle after passing through its apex the load is reduced on the lifter piston, and the internal spring returns the piston to its neutral state so the lifter can refill with oil. This small range of travel in the lifter's piston is enough to allow the elimination of the constant lash adjustment. It is desirable to keep debris out of the internal mechanism to ensure proper operation.
Even more sensitive than the lash adjusting function of the lifter is a valve deactivation system. Some internal combustion engines have valve deactivators on intake and/or exhaust valves on a pre-selected portion of engine cylinders. In a latched position, the valve deactivator is locked for normal operation of the valves. In an unlatched position, the lifter body is allowed to collapse and thereby fails to actuate the intake valves in engine cylinders in which an unlatch signal has been sent. The reason for deactivating a portion of cylinders is to achieve higher fuel efficiency by operating a fewer number of cylinders at a higher torque operating condition as opposed to operating all engine cylinders at a low torque operating condition, the latter of which is inherently less efficient in a spark-ignition engine. Movement of the latch assembly within the lifter is achieved by providing (or not providing) engine oil pressure in a fluid circuit dedicated for such control.
In some applications, pressurized oil for causing valve deactivation is provided to a lifter and the lost-motion or collapsible hardware is contained within the rocker arm such that the rocker arm collapses and fails to actuate the intake or exhaust valve with which it is associated. In either the case of the collapsing hardware being located in the rocker arm or in the lifter, the pressurized oil is provided to the lifter to access the collapsing hardware.
It is well known that regardless of measures taken to clean out machining and casting debris from an engine off the line, some debris remains. It has been found, particularly in the valve deactivator portion of the valve lifter (or rocker arm) such debris can cause malfunctions. Current strategies to prevent debris from entering the deactivator oil circuit within the valve lifter has been found to help; yet fails to be a guarantee for preventing debris ingress. Some way to protect the valve deactivator or rocker arm portion of the lifter and/or the valve lash adjuster portion of the lifter from being provided debris-contaminated engine oil is desired.